Technical Abstract:
Members of the tumor necrosis factor superfamily (TNFSF) are cytokines involved in diverse immunological and developmental pathways. Little is known about their evolution or expression in lower vertebrate species. Bioinformatic searches of available teleost databases including Zebrafish, Tetroadon, Fugu, and TIGR EST databases identified eleven unique genes containing a predicted TNF homology domain. Phylogenetic and synteny analyses indicated that seven genes have mammalian orthologs (CD40L, FASL, LIGHT, BAFF, APRIL, TWEAK, and EDA), while three have potential orthologs (RANKL-like, TRAIL-like, TNF-new), and one appears to be unique to teleosts (BAFF and APRIL like molecule designated BALM). We failed to identify orthologues of mammalian TNFSF members OX40L, CD27L, 4-1BBL, VEGI, CD30L, and GITRL. The mRNA expression of eight TNFSF ligand family members (CD40L, LIGHT, BAFF, BALM, FASL, RANKL-like, TRAIL-like, and TNF-new) were characterized in rainbow trout, Oncorhynchus mykiss, immune and non-immune tissues. In conclusion, eleven TNFSF members were identified in teleosts indicating early expansion of the family during vertebrate evolution. The absence of a number of TNFSF members involved in T cell function and secondary lymphoid organization correlate with morphological and functional differences between teleost and mammalian immune systems.